In many industrial applications, the tightening of threaded fasteners to a specific degree or torque is of extreme importance. For example, in the assembly of automobiles or aircraft, it is imperative that nuts, bolts, screws, lugs, and the like, are tightened to a pre-specified torque to ensure the resulting assembly functions properly not only at initial use, but over the long term. Moreover, it is not sufficient that the device simply be tightened as far as possible as this may result in stripping of the threads or vibrational problems in the resulting assembly.
Accordingly, it has long been known to use torque wrenches for tightening such devices. Such wrenches are not only able to rotate and tighten the device, but also provide the user with some sort of indication as to exact torque being applied. Such devices can be as straight forward as a bendable beam type wrench having a straight strain gauge thereon, whereby the user is provided with an indication as to the torque being applied by observing the degree of deflection of the bendable beam relative to the strain gauge. The strain gauge is provided with numbered graduations to provide the user with an accurate measurement.
In still further devices, it is known to provide the torque wrench in a ratchet type of assembly wherein each rotation or click of the ratchet represents a discrete level of torque being applied. However, such a device is normally not sufficiently accurate for the specifications being set forth by the automotive and aircraft industries which commonly employ such devices. More specifically, as each click represents only a discrete number of foot pounds, any movement between clicks will result in additional torque being applied, but not measured.
In still further torque wrench designs, known as shearing stress designs, sensors are mounted to a transducer of the wrench. The sensors measure the shearing stress being applied to the transducer as the wrench is rotated. A processor is provided on the wrench to then calculate the resulting torque based on the shearing stress being measured.
However, all currently known torque wrenches suffer from certain drawbacks resulting in less than optimal torque values and/or require an inordinate amount of time to use properly. For example, as the operator is rotating a fastener it becomes difficult for the operator to continue torquing the fastener while at the same time having to read the actual torque value on the torque value display. Similarly, the operator, in an attempt to reach the optimum torque value, may have to slowly proceed with small incremental increases in the applied torque until the optimal torque value is reached. It may take even a further amount of time if the operator is determined to achieve the exact prescribed torque value, even tough a variation of the prescribed or predetermined torque value is acceptable.